Tool for electrical connectors



aiia smff? Nov. 2, 1954 J. RKERCHNER ET AL 2,693,216

' TOOL FOR ELECTRICAL CONNECTORS Filed Oct. 11, 1951 X INVENTORS 40 $44JAY RALPH KERCHNER F BYwM. F. BRO-SKE United States Patent TOOL FORELECTRICAL CONNECTORS Application October 11, 1951, Serial No. 250,840

6 Claims. 01. 153-1 This invention relates to tools for pressurecrimping electrical connectors of the general type described in PatentNo." 2,535,013 to Freedom. s

In the electrical equipment industry and in other industries, it hasbeen recognized that soldered electrical connections, which have been sowidely used, have several disadvantages. are the difiiculties in makinga great number of electrical connections which are inexpensive and yetuniform, and doing so rapidly yet while maintaining excellent mechanicalstrength and electrical characteristics. To overcome these and otherdifiiculties of soldered connections, attention has been directedtowards the so-called pressure welded or crimped connectors wherein anenveloping metal barrel or ferrule is squeezed tightly onto a bare wireconductor so that the wire and the barrel are firmly adherent after thecrimping tool'is removed. f While various forms of crimped connectionshave been proposed and used there have arisen certain difiiculties anddisadvantages in some forms of these connections also. For example, insome crimped connections a single indentation is made to combine thebarrel and the conductor. This form of connection generallyv has poormechanical strength and it is difficult even for a skilled operator tomake successive crimps 'which are uniform. The double indent or W typecrimp as described in the above-mentioned patent has proven superior inservice, but the use of the present invention provides certainadvantages thereover, as explained here and after.

In making a double indent crimp (wherein two closely adjacentprojections or indentors are forced against a connector barrel which issupported in a generally conforming female die or nest), it has beenconsidered necessary to use a different sized male die or set of twoindenters with each barrel size one uses in order to obtain asatisfactory crimp for each of these various sizes. It is noted that .ithad been recognized that a given size nest could accommodate a specificsize ferrule which was adapted for use with a limited range of wiresizes.

Thus, for the broad range of wire sizes and the necessary ferrules usedin typical wiring systems, a multiplicity of male dies or indentors wererequired. This requirement is unsatisfactory in that either manyseparate tools are needed or else in a given tool or machine, the maledies would have 'to be changed frequently. Either of these contingenciesis undesirable; in the first instance a considerable investment fortools is needed and in the second instancetoo much time is likely to beexpended in changing dies. In either event, the tendency exists for theuser to employ the incorrect dies in a given operation due toinadvertence or through inertia. It is noted that a fairly casual-visualinspection of a crimp may fail to reveal that the desired structuralconfiguration of the crimp has not been fully attained.

In general, the double indentors for a crimping tool are made toexacting specifications and are machined to close tolerances and exactcurvatures, whereas the female dies or nests are considerably easier andless expensive to make. Thus, it is advantageous to minimize the amountof sets of indentors required for the usual ranges of wire sizes.

We'have found by constructing a set of double indenters and nests for aW crimp according to certain predetermined shapes and proportions thatthe range of wire sizes over which the tools may be used while stillattaining an effective crimp in the connection is substantiallyenhanced, so that a given set of two indenters approaches Prominentamong these. disadvantagesv 2,693,216 Patented Nov. 2, 1954 universalapplicability. We have also found that this improved construction tendsto strengthen the indenters so that breakage thereof is minimized, andfurther that superior connections may be produced.

Before describing the invention in detail, the requisites of aneffective crimp merit consideration in order that the features of theinvention may be more fully understood and appreciated. In crimping ametal barrel onto a bare conductor orconductors, the final crimp. shouldmeet, and preferably exceed, the minimum pull-out or tensile strengthvalues adopted by the various ofiicial standardization groups.Additionally, the torsion strength of the connection should be high lestthe conductors become loose by twisting and bending actions. Thecorrosion resistance of the connection should also be high to avoidchanges in the electrical characteristics of the connection; forexample, a small change in the resistance of a high current carryingconductor system is reflected in excessive power losses and evenoverheating of the connection. In general, the existence of voids or airspaces in the crimped connection tends to impair the corrosionresistance of the connection and voids should be kept to a minimum. Theexternal form of the connection should be symmetrical not only to avoidlocalized stresses but also so that standard size insulating sleeves, ifdesired, may be put on the connection without ditliculty. Sharp flaresor edges also are not desirable insofar as they tend to cut insulatingsleeves and are also objectionable electrically in that they may causevoltage breakdown due to corona discharge. A further factor is that thebarrel of the connection should not be sheared through or pierced. Sincemost barrels are tinned copper, ordinarily a visual test reveals thatshearing has occurred if the contrasting color of the conductors isvisible to the unaided eye.

By this invention the above mentioned advantages are attained whileminimizing the factors which are regarded as objectionable in a goodconnection.

The characteristics of the invention are brought out in the drawingswherein:

Fig. l is a perspective view of an electrical connection crimped by diesmade in accordance with one embodiment of the invention;

Fig. 2 is an enlarged sectional view taken transversely through theconnection of Fig. 1 and along the line 22 thereof;

Figs. 3, 4 and 5 are sectional elevations taken through a pair ofcrimping dies made according to this invention and these figures show aferrule and conductor within the dies in progressive stages of crimping;

Fig. 6 is an enlarged view showing the outlines of the dies of Figures35.

In Fig. 1 an electrical connector is generally indicated at 20 showing aring contact portion 22 and the ferrule portion 24. The ferrule portion24 is crimped over the bare conductor ends 26 of insulated wire 28.Substantially parallel indents or grooves 30 are shown in ferrule 24 asextending therein for the greater portion of the ferrule length andterminating a short distance (e. g. 5 from the respective ends of theferrule. Ends 30a of the indents 30 are shown as sloping graduallyupwardly from the greatest depth of the indent to the terminus of theindent.

Fig. 2 shows the characteristic W configuration of the cross-section ofthe crimp in Fig. 1 wherein the top of the central hump 34 is below thelevel of the top of the side horns 36. The conductors 26 are shown ascoined and extruded within the deformed ferrule 24. Thin sidewalledsections 35 of ferrule 24 extend downwardly from the centrally,depressed hump 34 having seam 34a. Folded and cold-worked beads or horns36 extend along the outer edges of the crimp while the bottom 37 of thecrimp conforms to the shape of the nest (see Fig. 3).

In Fig. 3 is shown the indenters 42of the male die 39 as they approachthe ferrule 24 as it lies in nest 44 of the female die 40. In this viewthe ferrule size shown is that of the smallest ferrule which may besatisfactorily usedwithin the range of the male die. Figs. 4 and 5depict partial and then completed crimping and emphasize the distortionachieved in cold working and flowing the ferrule 24 and conductors 26 toa cohesive mass.

3, Fig. 6 shows the construction of a'sp'ecific size nest 44 andindenters 42 in terms of dimensions which are:

E=the maximum width of the nest Fzthe maximum width of the ind'entor setD=the depth below the upper surface of the nest of the center of theradius of curvature of the greater portion of the nest- Szthe radius ofcurvature of the curved surfaces on the male die such as the ends oftheindenters L=the overall height of the indentors A=the distance from thebottomof each indentor to the bottom of the nest when the crimping diesare fully closed. This dimension largely determines the finalcross-sectional area of the crimped connection.

Referring to Figs. 2 and 6 it is to be noted that when the crimping iscompleted, the top of the central hump 34 is considerably. below thetopsof the" side horns 36. In other words, as Fig. 6 bringsout, thedistance X is less than the distance Y. Thus, as crimping pressure isexerted on the ferrule and conductor, the central top portions of theferrule and barrel are. coined and metal flows away from the centralhump towards the.

outer areas of the connection. We have found that by this arrangement,the indenters over a variety of barrel and wire sizes produce animproved distributionof the metal of the ferrule at the thin side-walledsections 35 and in the horns 36.

An additional feature of this invention is that the configuration of theouter, surface of'each indentor is so curved (or has a small straightportion) thatit is substantially parallel to the straight portion oftheadjacent parts of the nest cavity (see Fig. 6). This relationship ofsubstantial parallelism is maintained for the smallest size barrel forwhich a given indenting die is adapted.

We prefer to maintain the slope ofthe straight portion.

of the nest at about 18 from the vertical for the parallel relationshipand to decrease this slope for the larger wire sizes and ferrules withinthe given range, thus sacrificing parallelism somewhat. We also elongatethe straight portion of the nest (dimension D) substantially beyond theproportions indicated by Freedom. I

In designing for an optimum W crimp, we have found it desirable toconstruct the male dies and cooperating female nest so that thedimensions thereof yield a final cross-sectional area of thecrimp whichis about /3 of the original cross-sectional area of the metal in theferrule and the conductor or conductors. In other words, extrusion ofthe metal takes place longitudinally so that about /3 of the originalgross metal area is squeezed away from the crimp.

Regarding the range of wire sizes for which a given male die constructedaccording to this invention is .satis-. factory, we find that a givensize set of two indenters Will accommodate wire sizes from l68 AWG, thatthe next larger size is suitable for 6-2 AWG wire and the still largersize is useful in crimping conductors. from 1/0 through 4/0 AWG wire.The above ranges are illustrative of the flexibility of a male dieconstructed as described above; thus, one male die in the smaller wiresizes is suitable for crimping nine different sizes .of wire, which varyfrom about 2600 circular mils. in area to about 16,400an area range ofover 6 to 1. In crimp ing different sized Wires with the same indenterset-the ferrules (and of course the female dies) would preferably bechanged so that 16l4 AWG wires are used in one size ferrule, 12-10 AWGwires are used in a stilllarger ferrule and the 8 AWG wire isaccommodatedin the largest ferrule of this range.

As pointed out heretofore, it is desirable to avoid excessive voids inthe crimped connection. We have found that this may be minimized in thehorn section of the crimp by maintaining the distance between the outeredges of each indenter and the adjacent surface of the nestsubstantially the same over the range of ferrules used. With given rangefor a specific size tool, the substantially parallel relationshipdescribed above will be maintained, preferably by flattening the mouthof. the nests so that the slope thereof is about 18 from the vertical.But in the wider diameter ferrule as the radius of curvature of the nestincreases, the straight portion of the nest is brought upwards moreabruptly to compensate for the greater width of the nest, e. g. theslope from the verticalmay be about 16 or.l4 or even less. By thisarrangement the thickness of the horn section of the crimped connectionis maintained over a varietyv of sizes at about 100% of the originaluncrimped wall thickness of the ferrule.

It is a further feature of this invention that it permits the use notonly of thinner walled ferrules than have heretofore beenthoughtpossible but that it is feasible to use shorter barrels whilemaintaining a mechanically strong and electrically sound connection.This feature is of considerable interest due not only to the high costof. conductive metals such as copper, aluminum and tin but also becauseof their relative scarcity.

By following the teachings of this invention, satisfactory connectionsmay be made using various forms of conductors. Thus, theconductor metalmay vary in nature as well as the shape of the conductor; soft copper,hardened conductors, aluminum, etc., whether solid, round, square, ovalor stranded may be used. With solid rather than stranded conductors, itis sometimes found advisable to deform the conductor before crimping theconnection. This may be done,,for example, by presqueezing it to agenerally oval shape in cooperating cavities as are shown in Fig. 6'.With oval conductors, these should be positioned in the barrel withinthe nest so that the smaller or minor axis of the conductorisperpendicular to the bottom of the nest.

As pointed out above, in the optimum sizes very superior connections maybe made. For example, with a 4/0 size aircraft cable having a tensilestrength of approximately 550()' pounds, a single indent type crimpyields a connection having a tensile strength of approximately 20% ofthe cable strength 0n the other hand a W crimp on this same cable madeaccording to this invention exhibited a strength of about 45% of thecable strength. The advantages of this increased strength in terms ofsafety where the safetyv ofhuman lives and expensive equipment depend onperformance are selfevident. I

Havingnow particularly shown and described the invention what is claimedis:

1. Apparatus for producing laterally spaced longitudinal indentations ina wire-surround-ferrule which comprises a female. die member having anest cavity adapted to accommodate and receive the. ferrule.longitudinally therein, said nest cavity having on each sidebelow themouth thereof a pairof substantially straight forming sections extendingupwardly and inclined outwardly at a small angle to the vertical, afirst -motion-lirniting means connected'to said female nest die member,a male die member, and a second cooperating motion-limitingmeans'connected to said male die member and adapted to cooperate withthe first motion-limiting'means' when said die members are in the closeddie position to limit the motionof said die members toward eachother,,said male die member having a pairof laterally spacedlongitudinal indenters. projecting downwardly and including therebetweena longitudinal hollow, said indenters being adapted to enter saidnestcavity in spaced relation thereto with said indenters extendinglongitudinally of said nest cavity and with said indentersbeingoifsetlaterally to opposite sides of the center line of said nestcavity to indent the ferrule alongopposite sides of its axis, saidhollow included between said indenters extending upwardly .therebetweena significant distance so that said indenters and said hollow define inoutline a smooth W configuration with the top of said hollow betweensaid indenters being a substantial distance below the outer upper endsof said W configuration, whereby, in closing, the top of said hollowmoves down into said nest cavity a significant distance-below the upperlimits of said straight forming sections of the nest cavity before saidfirst and second motion-limiting means cooperate with eachother in theclosed die position to limit the motion of said die members toward eachother.

2. Apparatus for producing laterally spaced. longitudinal indentationsin a wire surrounding ferrule whichcomprises a female die member havinga nest cavity adapted to accommodate and receive the ferrulelongitudinally therein, said nest cavity having on each side below themouth thereof a pair of substantially straight forming sectionsextending upwardly and inclined outwardly at a small angle tothe.vertical, a first motion-limiting means connected to said female nestdie member, a male die member, and asecond cooperating motion-limiting:means connected to said male die member andadapted to cooperate with thefirst motion-limiting means when said die members are in the closed dieposition to limit the motion of said die members toward each other, saidmale die member having a pair of laterally spaced longitudinal indentersprojecting downwardly and including therebetween a longitudinal hollow,said indenters being adapted to enter said nest cavity in spacedrelation thereto with said indenters extending longitudinally of saidnest cavity and with said indenters being offset laterally to oppositesides of the center line of said nest cavity to indent the ferrule alongopposite sides of its axis, said hollow included between said indentersextending upwardly therebetween a significant distance so that saidindenters and said hollow define in outline a smooth W configurationwith the outer surface of each indenter being substantially parallel tothe respective adjacent straight forming section of said nest cavity andwith the top of said hollow between said indenters being a substantialdistance below the outer upper ends of said W configuration, whereby, inclosing, the top of said hollow moves down into said nest cavity asignificant distance below the upper limits of said straight formingsections of the nest cavity before said first and second motionlirnitingmeans cooperate with each other in the closed die position to limit themotion of said die members toward each other.

3. Apparatus for producing laterally spaced longitudinal indentations ina wire-surrounding ferrule which comprises a female die member having anest cavity adapted to accommodate and receive the ferrulelongitudinally therein, said nest cavity having on each side below themouth thereof a pair of substantially straight forming sectionsextending upwardly and inclined outwardly at a small angle to thevertical, a first stop element fixed with respect to said female nestdie member, a male die member, and a second cooperating stop elementfixed with respect to said male die member and adapted to contact thefirst-stop element when said die members are in the closed die position,said male die member having a pair of laterally spaced longitudinalindenters projecting downwardly and including therebetween alongitudinal hollow, said indenters being adapted to enter said nestcavity in spaced relation thereto with said indenters extendinglongitudinally of said nest cavity and with said indenters being ofisetlaterally to opposite sides of the center line of said nest cavity toindent the ferrule along opposite sides of its axis, said hollowincluded between said indenters extending upwardly therebetween asignificant distance so that said indenters and said hollow define inoutline a smooth W configuration with the outer surface of each indenterbeing substantially parallel to the respective adjacent substantiallystraight forming section of said nest cavity and with the tips of saidindenters being defined in outline by smooth curves and the hollowbetween said indenters being defined in outline by a smooth curve havingan effective radius of curvature less than the effective radius ofcurvature of the tips of said indenters.

4. Apparatus for producing laterally spaced longitudinal indentations ina wire-surrounding ferrule which comprises a female nest die memberhaving a longitudinally extending female nest cavity adapted toaccommodate and receive the ferrule longitudinally therein, said nestcavity having on each side below the mouth thereof a pair ofsubstantially straight forming sections extending upwardly and inclinedoutwardly at a small angle to the vertical, a first stop element fixedwith respect to said female nest die member, a male die member, and asecond cooperating stop element fixed with respect to said male diemember and adapted to contact the first stop element when said diemembers are in the closed die position, said male die member having apair of laterally spaced longitudinal indenters projecting downwardlyand including therebetween a longitudinal hollow, said indenters beingadapted to enter said nest cavity in spaced relation thereto with saidindenters extending longitudinally of said nest cavity and with saidindenters being offset laterally to opposite sides of the center line ofsaid nest cavity to indent the ferrule along opposite sides of its axis,said hollow included between said indenters extending upwardlytherebetween a significant distance so that said indenters and saidhollow define in outline a smooth W configuration with the outer surfaceof each indenter being substantially parallel to the respective adjacentstraight section of said nest cavity and with the top of said hollowbetween said indenters being a substantial distance below the outerupper ends of said W configuration, whereby, in closing, the top of saidhollow moves down into said nest cavity a significant distance below theupper limits of said straight forming sections of the nest cavity beforesaid first and second stop elements engage each other and stop said diemembers in the closed die position, and the extreme upper outer ends ofsaid W configuration being flared outwardly beyond a parallelrelationship with the respective adjacent straight forming sections ofthe nest cavity and said flaring ends of said W configuration beingclosely adjacent the upper limits of said substantially straight formingsections when said die members are in the closed die position, wherebysaid flaring'ends of said W configuration control the extrusion of theferrule upwardly along said straight forming sections of the nest cavityas said die members approach the closed die position.

5. Apparatus as claimed in claim 2 and wherein said small angle to thevertical is in the range from about 14 through about 18.

6. Apparatus as claimed in claim 2 and wherein said small angle to thevertical is about 18.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,109,837 Davis Mar. 1, 1938 2,275,163 Thomas Mar. 3, 19422,396,913 Carlson Mar. 19, 1946 2,535,013 Freedom Dec. 19, 19502,586,471 Matthysse Feb. 19, 1952 OTHER REFERENCES A-MP Catalogue,received at the Patent Ofiice on February 4, 1948 (page entitledSolistrand). (Copy in Division 14.)

